A molded article is typically produced in a mold cavity formed between an outer mold part and an inner or core mold part and also in the case of a complexly formed or undercut article by a side part. In a first step the thermoplastic material is filled in fluent condition into the inner mold part, then the outer part is pushed down in it to conform the thermoplastic mass into the desired shape. The outer mold part can be lined with a cover sheet that will form the surface of the finished molded body.
In German patent 865,365 of H. Kattwinkel a molding system is shown where part of the surface of the cavity of the inner mold half is formed by a spring-loaded piston. The plastic mass is pressed into the closed mold cavity to push back this piston and give the finished object the desired end shape.
German patent document 1,729,178 of B. Lohmann describes a system wherein a complicated system of demolding wedges can move at an angle to the molded body to strip it from the mold.
In German patent 3,043,275 of H. Mettenbrink a complexly shaped laminated article is made in a mold having a core that is made of several parts that can be moved relative to each other to allow demolding of the finished article.
German patent document 3,336,080 of F. Bielfeldt describes an injection-molding press for making glass or fiber-reinforced heat-curing bodies which has an injection piston that, in an upper position, blocks a fill passage for the resin. In a lower position the fill passage is unblocked for introducing the resin into the mold.
European patent application A2 186,015 of S. Masui describes a mold for making a laminated body where the mold halves are used to shear off the edges of the liner sheet.
In European patent application A2 331,447 of S. Okubo the liner skin is placed in one mold half and a body of the fill resin on the other half. The fill resin is melted and the two halves are pressed together to produce a laminated article.
British patent document 1,585,554 of O. olabisi two different liquefied resins are fed through a complex piston arrangement to the mold interior. The resultant article is webbed with the two resins intimately integrated with each other.
British patent application 2,227,707 of M. Osada puts a high-density pellet of a meltable synthetic resin in a mold, melts it, then forces it throughout the mold cavity.
All such system are fairly complex and do not allow the simple mass production of parts like a motor-vehicle instrument console which must have one surface formed by an attractive skin but have a body made of a softer resin. The mold must be completely closed around the plastic body before it is compressed, or special edges must be provided in the mold to prevent it from getting between the mating mold surfaces and preventing full closing of the mold.